Our goal is to study the mechanisms of immune defense against tumors. Over the past year we have carried out the following projects: (1)\studies on the biochemical mechanisms of macrophage activation; (2)\purification and characterization of a cytotoxic factor from activated macrophages; (3)\studies on the mechanisms of chemoattractant action of lysophosphatidylcholine on lymphocytes; (4)\studies on the mechanisms of action of interleukin 1; and (5)\characterization of monoclonal antibodies against human leukemia-associated antigens. (MB)